It is common to brake earthquake and wind induced structural movements by using supplemental dampers (which function to dissipate seismic and wind energy). This is particularly true when high amplitude or high frequency structural movements are expected. The brakes slow down and ultimately stop dynamic structural motion. Buildings and bridges with added dampers are safer and often more economical to construct in seismic and hurricane zones than those without dampers. Added dampers are also used to reduce seismic isolator displacements in structures.
At least three known mechanisms are typically utilized in such dampers: the viscosity of liquids or elastomers; metallic yielding; and coulomb friction. Each have been proposed or used in a different way. Each has its merits and drawbacks.
For instance, a liquid damper for construction needs special fluid, sealing, heat control and corrosion protection. It needs to be designed for infrequent, short duration, high power operation. One known liquid design is offered by Taylor Devices, Inc. These devices are, however, the most expensive of all dampers.
More economical, but less efficient, is a visco-elastomeric damper disclosed in Fyfe et al. U.S. Pat. No. 4,605,106 and available from the 3M company. Visco-elastomeric dampers, however, are bulky, aging and embrittling devices.
The third known alternative is a hysteretic damper utilizing steel yielders. Several such devices have been proposed but few are actually in use. One such steel yielder is disclosed in White U.S. Pat. No. 4,823,522.
The most economical and effective of all dampers rely on coulomb friction. These are unreliable, however, to the extent electrical and/or magnetic power sources are compromised. Teflon coated stainless steel bearings for seismic isolation and energy dissipation have also been proposed. However, these rely on gravity load and, as such, are not applicable as added dampers in interstory applications.
Popov et al. proposed a long slotted friction damped structural connection with copper linings and cup washer loading. While the Popov et al. damper appears to be a viable solution to structural damping, it is not a supplemental damper and not a device; rather, it has to be built with the structure as an integral part of it.
Because of the substantial expense associated with integrating dampers into new construction, supplemental dampers which can be retrofitted into existing buildings and structures are highly desirable. Indeed, the demand for supplemental seismic dampers for use in retrofitting applications is estimated to be over ten times greater than dampers used in new construction in the U.S. today.
Moreover, the hysteretic loop of typical friction devices is rectangular. Triangular and elliptical hysteretic loop shapes, however, may be more suitable for certain seismic applications. With rectangular hysteresis devices the lateral force is equally high at zero and at maximum support displacement. For elliptical hysteresis devices, on the other hand, at maximum displacement the lateral force is zero. That is ideal for many seismic applications. For different applications, however, it may be desirable to custom design the most suitable hysteresis loop shape.
A seismic damper design and methods and apparatus for installing the damper in a variety of applications is therefore needed which overcome the shortcomings of the prior art.